Reinforcing fillers such as carbon black, silica have long been used for reinforcing rubber or rubber reinforcement. Among these, silica, as compared with carbon black, has a property of a low tan .delta. at high temperatures (around 60.degree. C.) and a high tan .delta. at low temperatures (around 0.degree. C.), and therefore, when used for rubber compositions for tire treads, has the advantage capable of producing a tire having a low rolling resistance and a high gripping power. Silica, however, is inferior to carbon black in wear resistance and has a low electrical conductivity, and therefore, if used for tires, there is the problem that the tire will pick up a charge when driven on and will cause noise in the radio and other electronic equipments in the car and, in some cases, will cause their malfunction.
Covering the surface of the pigment etc. with, for example, silica to improve their dispersibility and to increase the weather resistance has been proposed in, for example, Japanese Examined Patent Publication (Kokoku) No. 50-14254 and Japanese Examined Patent Publication (Kokoku) No. 7-30269, but neither of these makes any reference to covering the surface of the carbon black used for reinforcing the rubber with silica.